1. Field of the Invention
The invention relates to a passive radiator having a chassis and a radiator body flexibly connected to the chassis and movable with respect to the chassis along a translation axis.
2. Description of the Related Art
International Patent Application No. WO-A 97/46047, corresponding to U.S. Pat. No. 5,892,184 (PHN 15.840), discloses a passive radiator which comprises a chassis, a mass element, and a sub-chassis extending between the mass element and the chassis. The mass element is movably fastened to the sub-chassis by means of a first resilient suspension ring, and the sub-chassis is movably fastened to the chassis by means of a second resilient suspension ring. The maximum axial excursion of the mass element is defined by the sum of the maximum axial excursions of each of the suspension rings. It has been found that in the case of uses requiring a comparatively high axial compliance in combination with a comparatively large axial excursion of the mass element, the suspension formed by the suspension rings may exhibit such distortions that undesired noises are produced in operation.
It is an object of the invention to improve the passive radiator of the type defined in the opening paragraph so as to counteract the generation of undesired noises.
This object is achieved with the passive radiator in accordance with the invention which comprises a chassis and a radiator body connected to said chassis and which is movable with respect to said chassis along a translation axis, the radiator body comprising a central mass element and at least one mass element which is arranged concentrically with respect to the central mass element, connection units being provided for movably interconnecting every two adjacent mass elements and for movably securing one of the mass elements to the element of the chassis, each of said connection units comprising two resilient annular connecting limbs, to which two connecting limbs two adjacent elements which form part of the said elements are secured, the connecting limbs of at least one of the connection units bounding a closed chamber which extends between the elements secured to said units and which is filled with a gaseous medium, the central mass element with its adjacent connection unit, as well as each concentrically arranged mass element with its adjacent connecting limb, forming a mass spring system, all the mass spring systems thus defined having at least substantially the same resonant frequency.
The use of two or more mass elements interconnected by resilient connecting limbs, also referred to as connecting rings, leads to a construction with a multiple suspension in which each mass element present contributes to the total air displacement during use. The connecting limbs are ring-shaped in view of their use. A mass element performs individual movements with respect to an adjacent mass element along the translation axis of the radiator body in operation, which results in displacements with respect to the chassis which are cumulations of individual movements. Comparatively large displacements of mass elements can be realized in this manner, so that considerable volume displacements can be achieved with a comparatively small radiator body. To counteract parasitic resonances and, as a consequence, the generation of undesired noises during use, the mass spring systems, present in the passive radiator according to the invention as defined above, have the same, or practically the same, resonance frequency. As a result of the use of one or more closed, i.e., impervious, chambers, translational movements of the radiator body produce pressure variations in the gaseous medium present between the connecting limbs of one or more connecting units. In the case of deflecting translational movements of the radiator body, these pressure variations are pressure rises, which have a favorable effect on the behavior of the suspension, particularly on the connecting limbs of the respective connecting unit or units. As a matter fact, these pressure rises result in pressure being exerted on the respective connecting limbs, which pressure issues from the closed chamber or chambers and prevents the connecting limbs from behaving in an unstable manner, such as flapping, fluttering or buckling, and thus producing undesired noises. This measure furthermore has the advantage that thin connecting limbs can be used, which enables a high axial compliance, i.e., a low stiffness, of the suspension formed by the connecting limbs to be achieved in the directions of translation of the radiator body. Decisive factors for the overall axial compliance of the whole arrangement are, particularly, the compliance of the medium in the closed chamber or chambers, and the resistance to deformation of the suspension. As the gaseous medium, a gas, air or another gas mixture may be used.
An embodiment of the passive radiator in accordance with the invention is characterized in that the connection units allow mainly movements of the mass elements along the translation axis of the radiator body, and counteract other movements. In this embodiment, it is prevented that the mass elements perform undesired tilting movements with respect to one another during operation, which tilting movements could lead to distortions in the sound reproduction. The annular connecting limbs used may be made from resilient materials which are known per se, such as, polyurethane or rubber, and preferably have a folded or corrugated structure.
An embodiment of the radiator in accordance with the invention is characterized in that a sealed chamber extends at least between the connecting limbs of the connection unit which adjoins the central mass element.
The embodiment of the radiator described above is preferably characterized in that the central mass element has a projection which extends to a location between the connecting limbs of the connection unit which adjoins the central mass element. The use of this characteristic feature results in a reduction of the closed chamber, which leads to greater pressure variations when the radiator body moves. An advantage of this that very thin connecting limbs can be used, preferably membranous limbs. Preferably, the projection is annular.
An embodiment of the radiator in accordance with the invention is characterized in that the sealed chamber contains a damping means for damping movements of the gaseous medium. The use of this characteristic feature enables the mechanical Q factor of the mass-spring systems to be reduced, as a result of which, any mutual resonances are damped out very effectively.
In the embodiment described above, the damping means preferably comprises an annular body of a porous material, for example, a cellular material, such as, a polyurethane foam. Such a material has a structure of small open cells. In operation, i.e., while the radiator body performs a translation, a gaseous medium present in the closed chamber flows through the cellular structure. This flow presents a mechanical resistance to translational movements of the radiator body with respect to its environment.
A practical embodiment of the radiator in accordance with the invention is characterized in that the annular body of a porous material forms part of the central mass element of the radiator body. The annular body may then be a part secured to the central mass element. The central mass element may be provided with a tuning mass, for which purpose a recess or cavity may be provided.
An embodiment of the radiator in accordance with the invention is characterized in that the number of mass elements is two, three or four. Although it is possible to use more mass elements, it has been found that a construction using two, three or four mass elements is satisfactory and can well be realized in practice in order to obtain a reliable radiator which is free from undesired noises and has a large excursion.
An embodiment of the radiator in accordance with the invention is characterized in that the shapes of the connecting limbs are identical to one another. This embodiment is to be preferred if it is an object to give each mass element the same maximum axial excursion with respect to its adjacent mass element or adjacent mass elements. In a practical embodiment, the connecting limbs may be, for example, omega-shaped. Any further connecting limbs are preferably arranged mirror-inverted positions with respect to each other for reasons of symmetry, so as to prevent asymmetry in the excursions and amplitudes of the mass elements.
An embodiment of the radiator according to the invention is characterized in that at least a number of the connecting limbs are of mutually different sizes, said sizes increasing in a direction away from the central mass element. By this measure, it is achieved that in relative terms, i.e., relative to its adjacent centrally disposed or more centrally disposed mass element, an annular mass element can perform a greater maximum relative displacement. An advantage of this configuration is that the connection units are utilized in an optimum manner without the deflections causing any undesired deformations of the connecting limbs.
The invention further relates to a loudspeaker system comprising an enclosure or cabinet which accommodates an electrodynamic loudspeaker and a passive radiator. The loudspeaker may be of any type which is known per se. The passive radiator present in the loudspeaker system according to the invention is constructed as defined above. The connection units of the passive radiator in the system according to the invention, allow well-defined mutual displacements of the mass elements under the influence of pressure variations in the enclosure, these displacements resulting in comparatively large air displacements, thereby enabling a comparatively high sound pressure to be achieved. Under the influence of pressure variations in the enclosure, the various connection units in such a system allow excursions which are fully adapted to the total moving mass of the radiator and the tuning frequency, the so-called Helmholtz resonance, of the system. For the above-mentioned reason, the resonant frequency of the mass spring systems that have been provided is preferably equal to the Helmholtz frequency of the enclosure including the loudspeaker and passive radiator, in the case that the system in accordance with the invention has 2 mass elements.
The invention further relates to an apparatus for presenting audible and, at option, visible information, the apparatus in accordance with the invention including the loudspeaker system in accordance with the invention. Such an apparatus is, for example, an audio-video or multi-media apparatus.